Application of improved vacuum degassing technique to refinement of heat resistant steel P91

An effective vacuum melting technique based on the improved vacuum degassing technique was used to produce thick-walled seamless pipes of 9Cr-IMo-V-Nb-N martensitic heat resistant steels in order to reduce the contents of harmful impurity such as oxygen, phosphorus. Then the pipe was heat treated by using optimized process technique. Both static and dynamic mechanical properties at room temperature and 566°C were measured respectively and evaluated by means of comprehensive analysis of standard deviation and statistic test. The results show that the comprehensive mechanical properties of this pipe are much better than those of pipes untreated with the improved vacuum degassing technique and heat-treated by using original heat-treatment process and almost the same as those of imported P91 thick-walled seamless steel pipe.